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How to Talk to a Climate Skeptic: Responses to the most common skeptical arguments on global warming

 

‘The null hypothesis says warming is natural’–An inappropriate test, and one that would fail anyway

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Natural variability is the null hypothesis; there must be compelling evidence of an anthropogenic CO2 warming effect before we take it seriously.

Answer: The null hypothesis is a statistical test, and might be a reasonable approach if we were looking only for statistical correlation between increasing CO2 and increasing temperature. But we’re not — there are known mechanisms involved whose effects can be predicted and measured. These effects are the result of simple laws of physics, even if their interactions are quite complex.

- 8 years ago

‘Climate is always changing’–That doesn’t mean it isn’t different today

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Climate has always changed. Why are we worried now, and why does it have to be humans’ fault?

Answer: Yes, climate has varied in the past, for many different reasons, some better understood than others. Present-day climate change is well understood, and different. Noting that something happened before without humans does not demonstrate that humans are not causing it today.

- 8 years ago

‘Natural emissions dwarf human emissions’–But emissions are only one side of the equation

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: According to the IPCC, 150 billion tonnes of carbon go into the atmosphere from natural processes every year. This is almost 30 times the amount of carbon humans emit. What difference can we make?

Answer: It’s true that natural fluxes in the carbon cycle are much larger than anthropogenic emissions. But for roughly the last 10,000 years, until the industrial revolution, every gigatonne of carbon going into the atmosphere was balanced by one coming out.

What humans have done is alter one side of this cycle. We put approximately 6 gigatonnes of carbon into the air but, unlike nature, we are not taking any out.

- 8 years ago

‘The CO2 rise is natural’–No skeptical argument has been more definitively disproven

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: It’s clear from ice cores and other geological history that CO2 fluctuates naturally. It is bogus to assume today’s rise is caused by humans.

Answer: We emit billions of tons of CO2 into the air and, lo and behold, there is more CO2 in the air. Surely it is not so difficult to believe that the CO2 rise is our fault. But if simple common sense is not enough, there is more to the case. (It is worth noting that investigation of this issue by the climate science community is a good indication that they are not taking things for granted or making any assumptions — not even the reasonable ones!)

- 8 years ago

‘We are just recovering from the LIA’–Why should we expect this to happen?

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Today’s warming is just a recovery from the Little Ice Age.

Answer: This argument relies on an implicit assumption that there is a particular climatic baseline to which the earth inexorably returns — and thus that a period of globally lower temperatures will inevitably be followed by a rise in temperatures. What is the scientific basis for that assumption?

- 8 years ago

‘Climate scientists dodge the subject of water vapor’–No, they really don’t

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Climate scientists never talk about water vapor — the strongest greenhouse gas — because it undermines their CO2 theory.

Answer: Not a single climate model or climate textbook fails to discuss the role water vapor plays in the greenhouse effect. It is the strongest greenhouse gas, contributing 36% to 66% to the overall effect for vapor alone, 66% to 85% when you include clouds. It is however, not considered a climate “forcing,” because the amount of H2O in the air basically varies as a function of temperature.

- 8 years ago

Water vapor is indeed a powerful greenhouse gas, but there is plenty of room for CO2 to play a role

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: H2O accounts for 95% of the greenhouse effect; CO2 is insignificant.

Answer: According to the scientific literature and climate experts, CO2 contributes anywhere from 9% to 30% to the overall greenhouse effect. The 95% number does not appear to come from any scientific source, though it gets tossed around a lot.

- 8 years ago

There is no proof in science, but there are mountains of evidence

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Correlation is not proof of causation. There is no proof that CO2 is the cause of current warming.

Answer: There is no “proof” in science — that is a property of mathematics. In science, what matters is the balance of evidence, and theories that can explain that evidence. Where possible, scientists make predictions and design experiments to confirm, modify, or contradict their theories, and must modify these theories as new information comes in.

- 8 years ago

‘CO2 doesn’t lead, it lags’–Turns out CO2 rise is both a cause and an effect of warming

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: In glacial-interglacial cycles, CO2 concentration lags behind temperature by centuries. Clearly, CO2 does not cause temperatures to rise; temperatures cause CO2 to rise.

Answer: When viewed coarsely, historical CO2 levels and temperature show a tight correlation. However, a closer examination of the CH4, CO2, and temperature fluctuations recorded in the Antarctic ice core records reveals that, yes, temperature moved first.

Nevertheless, it is misleading to say that temperature rose and then, hundreds of years later, CO2 rose. These warming periods lasted for 5,000 to 10,000 years (the cooling periods lasted more like 100,000 years!), so for the majority of that time (90% and more), temperature and CO2 rose together. This remarkably detailed archive of climatological evidence clearly allows for CO2 acting as a cause for rising temperatures, while also revealing it can be an effect of them.

- 8 years ago

‘Geological history does not support CO2′s importance’–Just not true

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Over the last 600 million years, there hasn’t been much correlation between temperatures and CO2 levels. Clearly CO2 is not a climate driver.

Answer: While there are poorly understood ancient climates and controversial climate changes in earth’s long geological history, there are no clear contradictions to greenhouse theory to be found.

- 8 years ago

‘Historically, CO2 never caused temperature change’–Not so

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: In the geological record, it is clear that CO2 does not trigger climate changes. Why should it be any different now?

Answer: Given the fact that human industrialization is unique in the history of planet earth, do we really need historical precedent for CO2-triggered climate change before we accept what we observe today? Surely it is not far-fetched that unprecedented consequences would follow from unprecedented events.

But putting this crucial point aside, history does indeed provide some relevant insights and dire warnings.

- 8 years ago

‘It’s the sun, stupid’–Very bright, yes, but not getting brighter

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: The sun is the source of warmth on earth. Any increase in temperature is likely due to changes in solar radiation.

Answer: It’s true that the earth is warmed, for all practical purposes, entirely by solar radiation, so if the temperature is going up or down, the sun is a reasonable place to seek the cause.

- 8 years ago

The problem is not how high the temperature may go, but how fast it is changing

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: The earth has had much warmer climates in the past. What’s so special about the current climate? Anyway, it seems like a generally warmer world will be better.

Answer: I don’t know if there is a meaningful way to define an “optimum” average temperature for planet earth. Surely it is better now for all of us than it was 20,000 years ago when so much land was trapped beneath ice sheets. Perhaps any point between the recent climate and the extreme one we may be heading for, with tropical forests inside the arctic circle, is as good as any other. Maybe it’s even better with no ice caps anywhere.

It doesn’t matter. The critical issue is not what the temperature is, or may be, or will be. The critical issue is how fast it is moving.

- 8 years ago

‘Kyoto is a big effort for almost nothing’–Kyoto is only in its first phase

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: The Kyoto treaty, even if fully implemented, would only save us about a tenth of a degree of future temperature rise many decades from now. What a waste of effort! You can see for yourself here at the Junk Science website.

Answer: There are three big problems with this claim.

- 8 years ago

China and India have joined Kyoto, they just have different obligations, as is morally appropriate

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Why should the U.S. join Kyoto while India and China haven’t?

Answer: The U.S. puts out more CO2 than any other nation on earth, including China and India, by a large margin. Considering the relative populations (a billion-plus each for China and India versus 300 million in the U.S.), per capita emissions in the U.S. are many times larger. This has been true for the past 100-plus years of CO2 pollution.

For the U.S. to refuse to take any steps until India and China do the same is like the fattest man at the table, upon realizing the food is running out, demanding that the hungry people who just sat down cut back just as much as him, at the same time.

- 8 years ago

‘Climate change mitigation would lead to disaster’–Not really, but this may be lesser of two evils

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: The kind of drastic actions required to mitigate global warming risk the destruction of the global economy and the deaths of potentially billions of people.

Answer: Is this supposed to mean the theory of anthropogenic global warming must be wrong? You can not come to a rational decision about the reality of a danger by considering how hard it might be to avoid. First things first: understand that the problem is real and present.

- 7 years ago

Only if you ignore fossil fuel emissions

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: The United States absorbs more CO2 into its land than it emits into the air. The world should be grateful.

Answer: As often the case, at the heart of this talking point is a grain of truth. But it does not serve the purpose for which it’s been enlisted. According to the U.S. Department of Energy land-use changes in the U.S. between 1952 and 1992 have resulted in a net absorption of CO2. But this is only true of natural CO2 — the natural flux of CO2 into and out of forests and peat bogs and soil, as well as carbon that’s been sequestered as lumber and other wood products. These fluxes are actually much larger than anthropogenic emissions, but they go both ways, whereas fossil fuel burning only emits carbon.

- 7 years ago